 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.internal.handlers;

 import org.eclipse.core.commands.AbstractHandler;
 import org.eclipse.core.commands.ExecutionEvent;
 import org.eclipse.ui.PlatformUI;
 import org.eclipse.ui.help.IWorkbenchHelpSystem;

 /**
  * Displays the help resource specified in the <code>href</code> command
  * parameter or simply displays the help bookshelf if no parameter was passed.
  *
  * @since 3.2
  */
 public final class DisplayHelpHandler extends AbstractHandler {

     /**
      * The identifier of the command parameter for the URI to oepn.
      */
     private static final String PARAM_ID_HREF = "href"; //$NON-NLS-1$

     public final Object execute(final ExecutionEvent event) {
         final IWorkbenchHelpSystem helpSystem = PlatformUI.getWorkbench()
                 .getHelpSystem();
         final String href = event.getParameter(PARAM_ID_HREF);

         if (href == null) {
             helpSystem.displayHelp();
         } else {
             helpSystem.displayHelpResource(href);
         }

         return null;
     }
 }

